Lower Silurian polychaetaspid polychaetes from Gotland, Sweden

The Silurian tropical sea in the Gotland area was inhabited by a rich and varied polychaete fauna, which has been studied at the two sections Lusklint 1 and Lickershamn 2. The sections comprise the three stratigraphically oldest units on Gotland, the Lower Visby Beds, the Upper Visby Beds, and the Högklint Beds, which are exposed in the northwestern part of the island and range in age from latest Llandovery to early Wenlock. Polychaetaspid polychaetes with the two genera Oenonites and Kozlowskiprion constitute a large and diverse group but their occurrence on Gotland has hitherto only been noted. The generic name Polychaetaspis Kozlowski, 1956 is a junior synonym to Oenonites Hinde, 1879, and therefore rejected. The type specimen of O. curvidens Hinde, 1879 is redescribed. The first maxillary pieces (MI's), have been of greatest interest when reconstructing jaw apparatuses. Identification of the species is based on isolated jaw elements (scolecodonts) and apparatuses, utilizing a biological species concept. Five new species are introduced: Oenonites olavi n. sp., O. zappae n. sp., O. eichwaldi n. sp., O. jennyensis n. sp., and O. wejstorpi n. sp. The remaining three taxa include O. latus (Kielan‐Jaworowska 1966), O. cf. wyszogrodensis (Koztowski 1956), and Kozlowskiprion longicavernosus Kielan‐Jaworowska, 1966. The taxonomic diversity is highest in the Högklint Beds (unit b) and most of the species studied indicate a preference for warm and shallow marine environments. Only the two species K. longicavem‐osus and O. latus are present through the entire sections from the Lower Visby Beds to the Högklint Beds, and these are presumably more tolerant to environmental changes and show a preference for a deeper‐water habitat. The relationship between the Gotland and Baltic polychaet‐aspids is discussed. One left jaw element with reversed asymmetry referred to O. jennyensis was recovered.